The invention concerns a magnet coil system comprising                at least one coil section, wound with a high temperature superconducting (=HTSL) tape conductor,        and a low temperature superconducting(=LTS) wire,the HTSL tape conductor and the LTS wire being electrically connected in series.        
Such a magnet coil system is known e.g. from DE 10 2004 007 340 A1 (=U.S. Pat. No. 7,157,999).
Superconductors are able to carry electrical currents essentially without ohmic losses. In particular, they are used wherever high electric current strengths are needed, e.g. in magnet coils.
Generally, magnet coils make use of two types of superconductors. Metallic low temperature superconductors (LTS), as NbTi or Nb3Sn are usually wires containing filaments of the LTS material. Ceramic high temperature superconductors (HTS or HTSL), e.g. of the ReBCO type, usually comprise an HTS layer on a tape-like substrate, for example a steel tape. HTSL superconductors of the BSCCO type have also usually the shape of a tape. However, they comprise like the LTS conductors filaments, usually embedded in a silver matrix.
DE 10 2004 007 340 A1 (=U.S. Pat. No. 7,157,999), proposes a magnet field system with radially stacked partial coils, an LTS partial coil and an HTS partial coil being electrically connected in series via an LTS-HTS joint. No details concerning the joint design are disclosed.
A joint effects a transfer of current between two superconductor parts. Thereby it is technically demanding to achieve a current transfer between the superconductor parts that is really superconducting. Often an in fact extremely small but noticeable ohmic resistance at a joint has to be accepted. The latter is in particular true for joints between LTS and HTS materials. Such ohmic resistances can in particular lead to a disruptive drift during persistent mode operation of a magnet coil system.
The basic purpose of the invention is to achieve in an easy way an acceptably small remaining ohmic resistance in a magnet coil system of the above mentioned kind. In particular, the magnet coil system should allow a sufficiently small drift during operation in persistent mode.